1. Field of the Invention
The present invention relates to an energy conservation system for chilled-product vending machines. More specifically, the present invention relates to a control circuit for a convection type refrigeration system for a vending machine which dispenses chilled products such as beverage cans or bottles.
2. Description of the Prior Art
Heretofore, in refrigeration systems of vending machines including a compressor, a condenser, evaporator coil and an evaporator fan, the compressor has been cycled ON and OFF under the control of a thermostat, and the evaporator fan, which blows air over the evaporator coil to circulate chilled air throughout the vending machine, has been run continuously even during the periods when the compressor was OFF. The unnecessary high energy usage and waste caused by the continuous running of the evaporator fan or fans, has become a problem with the current high cost of energy. One logical solution to reducing the consumption of energy is to cycle the evaporator fan motor ON and OFF with the compessor thus decreasing the running time of the evaporator fan. However, this approach causes several problems, the discovery of which are part of the present invention.
Firstly, if the evaporator fan is cycled off in synchronism with the turning OFF of the compressor, freeze up of the evaporator coil can occur in humid, high temperature conditions. Secondly, by keeping the evaporator fan shut off during the compressor off cycles, large variations in temperature in the vending machine occur, creating large variations in temperature of the next to be vended products. Also, during this off period of the evaporator fan, large variations of temperature occur throughout the vending machine due to lack of air flow, and temperatures sensed by the thermostat which controls the compressor cycling are less accurate than desirable. Thirdly, when vending machines are located in below freezing environments, (32.degree. F.) an idyl condition of the evaporator fan may permit the chilled products to freeze. That is, when the evaporator fan is running and blowing air over the evaporator coil and throughout the vending machine, this flow of air dissipates heat generated by the evaporator fan motors thus acting as a heater to prevent the stored products from freezing. Thus, the aforementioned problems exist when the evaporator fan is permitted to cycle on and off with the compressor, even though a substantial reduction in energy consumption results.
Accordingly, a need in the art exists for a system which will reduce the consumption of energy in the refrigeration system of a vending machine, but will at the same time solve the aforementioned problems of evaporator coil freeze up in high, humid temperature conditions; product freeze up in below freezing environmental conditions; and large variations in next to be vended products and temperature distribution throughout the vending machine.